1. Field of the Invention
The present invention relates to a conveyor belt made of rubber or a rubber-like plastic, with tension supports based on a fabric (warp, weft) made of textile materials (e.g. polyester warp, polyamide weft) or a synthetic cord fabric (e.g. polyester cord, polyamide auxiliary weft). The supports are embedded in the conveyor belt and extend in the longitudinal direction, whereby the fabric or cord fabric is arranged in one or two multiple layers, in particular in two or three layers, with or without an intermediate rubber coating. The belt is closed by overlapping its longitudinal edges to form a tubular belt supported by rollers or the like.
2. The Prior Art
German Patent DE-C-943,817 discloses a hose belt conveyor which did not initially find wide application. However, this closed conveyor system has been further developed during the last 10 years. Within the inlet and outlet sections, the conveyor belt forms a trough in the same way as conventional belt conveyors. However, the belt closes across the transport and return run sections, forming a tube (tubular conveyor belt, hose belt, roller belt).
The following equipment parts are required for this transport system: annularly arranged supporting rollers (German Patents DE-C-3,145,899 and DE-A-3,606,129), correction rollers (German Patent DE-C-3,122,664) and strands (e.g., top and bottom strands). As compared to the conventional belt conveyors, the closed transport system is characterized by the following advantages: it is particularly capable of traveling through curves, it has a particularly high ascent capability, it saves space, and it protects the conveyed material and the environment (e.g., when conveying dusty material). However, these advantages are weighed against great technical problems that accompany the development of the hose belt or tubular belt conveyor. This is demonstrated by the following state of the art.
According to German Patent DE-A-3,228,937 and German Patent DE-A-3,506,947, the conveyor belt has clamping strips or radially outwardly projecting, longitudinally extending bridges within the closing zone. This locking mechanism, however, has the drawback that an additional roller system (guiding rollers, pressure rollers) is required in addition to the supporting and correcting rollers. In addition, the clamping strips or bridges are susceptible to wear.
A conveyor belt is known from German Patent DE-C-2,944,448, which includes self-adhesive strips arranged on the overlapping sides of the belt. However, an adhesive closure within the overlapping zone has the following drawbacks: relative movements are not possible in the overlapping zone. Furthermore, an adhesive lock does not hold up under mechanical stress, and its function is highly impaired by soiling. Moreover, this closure has a greater tendency to freezing and consequently hinders the unfolding at the point of ejection. Similar problems occur also when locking lips are used (German Patent DE-A-2,800,454, and EP-c 046,690).
According to more recent developments, the tubular conveyor belt is formed by merely overlapping the longitudinal edges of the belt. In this connection, the conveyor belt according to German Patent DE-A-3,606,129 has stable supports (tension supports) in the form of steel wire ropes embedded in its marginal zones overlapping one another, with the ropes extending through in the longitudinal direction. The center part may contain reinforcing inserts extending in the transverse or diagonal direction (German Patent DE-A-3,612,765). This direction of development, however, shows a number of problems, which are described in greater detail below.
First, a conveyor belt is subjected to the greatest mechanical stress at the feeding point of the belt conveyor. Within this zone, the conveyor belt is in the flat to slightly trough-shaped condition. The material to be conveyed mainly impacts the center zone of the conveyor belt. The useful life of the conveyor belt depends on the load-bearing capability of the center zone of the belt. Diagonally arranged strips of fabric consisting of only one or two inserts and intermediate spaces filled only with rubber offer insufficient load-bearing capacity.
Second, overloading may occur in connection with belt conveyors. In this case, the trough-shaped conveyor belt accepts within the feed zone more material than can be accommodated in the tubular condition because of the smaller cross section of the belt in the tubular condition. With a weak reinforcing material, the belt tends to bulge outwardly. The conveyed material forcibly hits the supporting rollers, which may damage the conveyor belt or other parts of the conveyor system.
Third, the fabric inserts are embedded by vulcanization around the steel rope tension support. The tensile stress, almost totally across the ropes present in the marginal zone, as well as the repeated forced shaping to the tubular form (the belt has the tendency to fold open) on each supporting roller in the direction of travel lead to a high mechanical stress in the marginal zone of the belt. This is increased even further by torsion when the belt travels through curves unless another solution, for example, rotatable roller frames, is provided.
Fourth, by limiting the tension supports to the narrow marginal zones of the belt, high strength (tensile strength) belts cannot be formed, or such belts can be formed only if other conveyor belt parameters (e.g. thinner cover plates) are accepted.
Now, a conveyor belt is known from European Patent EP-B-336,385, which has the following tension support variations:
(I) The tension supports consist exclusively of ropes of individual cords which, in the overlapping zone, have a different spacing from each other and/or a different diameter than in the remaining zone of the belt. PA1 (II) The tension supports consist exclusively of warp threads formed with weft threads of a fabric, whereby the fabric has a different structure or make-up in the overlapping zone than in the remaining zone of the belt. PA1 (III) In the overlapping zone, the tension supports consist of aramide ropes or individual aramide cords, whereas the tension supports in the remaining zone of the belt are exclusively warp threads, formed with weft threads of the fabric.
The invention is based on a further development of the belt based on tension support variation II. Tension support variation II continues to show considerable deficiencies with respect to guidance, namely in the open (i.e., trough-shaped) configuration and in the closed (i.e., tubular) configuration, as well as in the transition zone. Particularly disadvantageous is the fact that the reset forces fade quickly after a short period of operation. This finally leads to the fact that the sides of the belt hang into the center of the tube.